The field of the disclosure relates generally to process control loops and, more particularly, to a method and system for reducing ramp tracking errors of process control devices.
When designing control system inner loops to mitigate ramp tracking error of process control devices, a balance between transient tracking capability and steady-state stability can be difficult to maintain. A damped inner loop provides predictable stable results. However, transient tracking errors become more significant as inner loop ramp rates increase. This can drive a desire for more aggressive tuning of the inner loops to meet transient performance requirements. Aggressive gains and traditional feed-forward methods lead to overshoot and undesirable stability challenges.
Transient tracking of scheduled engine parameters is often a trade-off between inner loop stability and inner loop frequency response. Designing an inner loop system with the frequency response characteristics to have low transient tracking can result in a less stable, underdamped response with excess overshoot during transients.
A more stable inner loop design is damped or critically damped. While a critically damped inner loop is well behaved, transient tracking errors can be significant to the overall system design. A critically damped system has a response that lags the demand input. This lag typically correlates with a time delay of a deterministic amount. This time lag creates a transient tracking error that is directly proportional to the demand ramp rate.